The present invention relates in general to telephones and in particular to telephones intended for connection to a central switching system (CO or PABX) capable of responding to DTMF dial signals and loop breaks to execute special features or functions in addition to conventional directory number and tandem trunk dialing. More specifically, the invention relates to what are known as "electronic telephones" of the sort which can perform speed dialing and "last number dialed" operations, and brings improvements to the capabilities of such telephones.
It is known in the art to incorporate integrated circuit chips, including microprocessors with ROM and RAM, into telephone sets (or accessories which plug into such sets) in order to "automate" certain operations and provide user convenience. The most popular of these state-of-the-art telephones permit directory numbers to be written into memory and subsequently speed-dialed out in response to actuation of a single switch which starts a process of reading the successive dial digit values from memory. Others provide a "last number dialed" feature by which the digit values punched into a dialing key pad are written to memory, remembered, and subsequently reproduced on the phone line in response to actuation of a single switch. This is employed to "re-dial" after the user has attempted to dial another phone and received a busy signal.
As large, medium and small PABX systems (and even central office systems) have developed--with stored program control and digital switching--many special features or functions have become rather common. As only a few examples, those working in the industry are familiar with such features as "camp on", "call pick-up", "executive override", "hold and retrieve". Generally stated, these features are practiced by the user of a given telephone set by keying a certain combination of dial digit values called access codes or feature codes. These frequently require, however, that the user remember (or refer to a list) of such codes, and that he operate his hook switch at various points to signal a hook flask or a reseizure.